Vehicle evaporative emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy.
In a typical canister purge operation, a canister purge valve (CPV) coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve (CVV) coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
Diagnostics may be performed on the evaporative emission control system, e.g., to detect leaks in the system. Leak diagnostics may be based on pressure or vacuum changes in one or more components of the emissions control system during certain conditions. A common leak path in the emission control system is through the CPV, the result of canister carbon dust accumulation and sealing surface deterioration.
Responsive to an indication of a leaky CPV, mitigating action may be taken restore CPV functionality. For example US Patent Application No. 2014/0311461 A1 teaches under vacuum conditions, opening the CPV and generating pressure pulsations in a conduit coupled to the CPV while maintaining the CPV open such that contaminants may be dislodged and evacuated to the intake manifold. However, the inventors herein have recognized potential issues with such a method. In particular, in situations wherein a leaky CPV is still detected subsequent to mitigating action, considerable time may pass prior to the vehicle being serviced to repair the leaky CPV. During this period of time, when the engine is off, the travel path of least resistance for fuel tank vapor may be from the fuel tank to atmosphere via the leaky CPV. As such, fuel tank vapors may bypass the majority of the vapor canister, traveling instead through a small buffer area prior to exiting to the atmosphere via the leaky CPV. As the majority of the canister is bypassed as a result of the leaky CPV, adsorption is not optimal and increased emissions may result.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising, when an engine is off, routing fuel vapors from a fuel tank into a vapor adsorbent and venting said vapor adsorbent to atmosphere; when said engine is operating, venting said vapor adsorbent to atmosphere, and routing vapors from said fuel tank through a purge valve, and desorbed vapors from said vapor adsorbent through said purge valve, into said engine for combustion; and when said purge valve is detected as leaking and said engine is turned off, turning off said purge valve, isolating said canister form atmosphere, and re-routing said vapors in said tank first through said vapor adsorbent and then to said purge valve. In this way, responsive to an indication of a leak in said purge valve, fuel tank vapors may be routed such that vapors may first travel through the vapor canister where they may be efficiently adsorbed, en route to engine intake via the leaky CPV prior to exiting to atmosphere.
In one example, re-routing said vapors in said tank through said canister and to said purge valve includes changing a position of a first two-way valve positioned between a canister vent port and a canister vent valve, changing a position of a second two-way valve positioned between a canister purge port and said purge valve, and closing said canister vent valve. As such, responsive to an engine-off event wherein a leak in the purge valve is indicated, by changing the position of said first and second two-way valves, and closing said canister vent valve, fuel tank vapors may be prevented from traveling from said fuel tank to engine intake prior to being adsorbed by said vapor canister. In this way, responsive to an indication of a leaky purge valve, excessive release of fuel tank vapor to the atmosphere may be prevented during engine-off conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.